Can anyone with some Hivi M6a's lying around test this for me?

[Sdiver2489]

Hello all,

I just noticed that when I play a sine wave test tone into these at a loud enough volume(just a little above "normal") I get quite a bit of distortion. Basically it sounds like a "buzzing".

Can anyone test theirs for me as I don't want to purchase new ones if this is the "norm".

EDIT: The buzzing is most noticeable at multiples of 420 Hz or so. It only is apparent, as I said, at a fairly high volume.

[joecarrow]

According to the spec sheet, the metal cone breakup is around 3500 hz. You can see this as a peak in the response and a wiggle in the impedance graph.This means that if you're playing a 840 hz sine wave, the 4th order distortion products could excite the cone breakup. That's just a fact of life with stiff cones, but the Hi Vi M8a has been used around here before due to peoples' opinion that for a metal cone it's fairly well behaved. Its a good thing that its distortion due to cone breakup is well controlled and predictable.

The general practice is to cross low enough that 3rd order (or at least second order) products don't excite the resonance, and also to include a notch filter at the breakup frequency.

[Sdiver2489]

According to the spec sheet, the metal cone breakup is around 3500 hz. You can see this as a peak in the response and a wiggle in the impedance graph.This means that if you're playing a 840 hz sine wave, the 4th order distortion products could excite the cone breakup. That's just a fact of life with stiff cones, but the Hi Vi M8a has been used around here before due to peoples' opinion that for a metal cone it's fairly well behaved. Its a good thing that its distortion due to cone breakup is well controlled and predictable.

The general practice is to cross low enough that 3rd order (or at least second order) products don't excite the resonance, and also to include a notch filter at the breakup frequency.

My crossover is positioned at about 1600 Hz and is fourth order. I assumed that would be enough to take care of that. It doesn't appear like the breakup is as significant on the M6a as it is on the M8a. I know when I measured the speaker I was seeing other frequencies than just 3500 Hz. I suppose I may have to consider adding one at some point as my crossovers are already constructed.

[joecarrow]

If the resonance is at 3400 hz, it's only one octave above 1600 hz. 4th order is 24 db/octave, so it's only 24 db down at resonance- assuming that your crossover accounts for driver impedance properly and is really giving you a 24 db/octave slope. Also, the second order distortion from the 1600 hz signal (which is generated in the motor, so no crossover can filter it out) is present. If the crossover was steeper and lower, say 30db down by 1600 hz, you'd probably have noticably better performance.

If you look at the design threads for the Modula MTM, Natalie Portman, and Modula MT, you'll see a great deal of discussion about this kind of thing. Jon Marsh's designs use an unconventional (elliptic) crossover with really steep slopes- something like 6th to 8th order- for the first octave or so. They're a bit more sophisticated than just using a notch, but a well executed notch with a regular crossover is still an extremely valid way to get the most out of a metal cone driver. One of the major advantages of Jon's elliptic approach is to reduce the component count and total cost.

I hope that's of some help- I think you can do fine with these drivers if you recognize their limitations, the best way around them, and whether or not it really impacts your listening. If it shows up in music, that's one thing, but if it really takes a concentrated sine wave at high level to show up- it might not be worth fixing unless you like to listen to that kind of thing.

[Sdiver2489]

If the resonance is at 3400 hz, it's only one octave above 1600 hz. 4th order is 24 db/octave, so it's only 24 db down at resonance- assuming that your crossover accounts for driver impedance properly and is really giving you a 24 db/octave slope. Also, the second order distortion from the 1600 hz signal (which is generated in the motor, so no crossover can filter it out) is present. If the crossover was steeper and lower, say 30db down by 1600 hz, you'd probably have noticably better performance.

If you look at the design threads for the Modula MTM, Natalie Portman, and Modula MT, you'll see a great deal of discussion about this kind of thing. Jon Marsh's designs use an unconventional (elliptic) crossover with really steep slopes- something like 6th to 8th order- for the first octave or so. They're a bit more sophisticated than just using a notch, but a well executed notch with a regular crossover is still an extremely valid way to get the most out of a metal cone driver. One of the major advantages of Jon's elliptic approach is to reduce the component count and total cost.

I hope that's of some help- I think you can do fine with these drivers if you recognize their limitations, the best way around them, and whether or not it really impacts your listening. If it shows up in music, that's one thing, but if it really takes a concentrated sine wave at high level to show up- it might not be worth fixing unless you like to listen to that kind of thing.

You mean I am the only one that rocks out to 420 Hz?

;b>